The present invention relates to an improvement in an ultrasonic motor having an oscillation drive circuit for forming an excitation signal based on excitation of a piezoelectric element and an electronic apparatus having an ultrasonic motor.
In recent times, ultrasonic motors producing driving force by making use of the piezoelectric effect of a piezoelectric element have attracted attention in the field of micromotors. The ultrasonic motor is a motor making use of a mechanical resonance phenomenon, a drive frequency thereof is varied by environmental temperature or outside load and accordingly, there is needed a complicated drive circuit such that a frequency tracking function is added to an outside oscillator or the like. However, an oscillator bonded with a piezoelectric element can simply be driven by making use of oscillation drive system for driving the oscillator by self-excited oscillation.
As an example of an oscillation drive circuit making use of such self-excited oscillation, as shown by FIG. 23, there has been known a type having a piezoelectric element 102 to be excited, a 3-state inverter 502 as well as 3-state buffers 501a and 501b for amplifying an initial signal based on the excitation to an excitation signal and condensers 505 and 506 for setting the excitation signal to a predetermined frequency (refer to JP-A-8-251952).
Further, a flection standing wave is caused in an oscillator 101 bonded to the piezoelectric element 102 and frictional force is exerted to a moving body (not illustrated) pressed to the oscillator 101 to thereby rotate the moving body in a predetermined direction.
However, according to an oscillation drive circuit 405 making use of self-excited oscillation as mentioned above, when the circuit is restarted after the oscillation drive has been stopped, there poses a problem of remaining electric charge of the condensers 505 and 506 or a problem in which even when the 3-state inverter 502 as well as the 3-state buffers 501a and 501b are brought into an active state, both of a Pch transistor and an Nch transistor are brought into an OFF state, that is, an output is brought into a high impedance state which is caused by a dispersion in the semiconductor process, and there poses a problem in which an initial signal constituting a basis of self-excited oscillation becomes difficult to produce in the oscillation drive circuit 405, much time is required to rise of oscillation, further, failure of starting oscillation is resulted and so on to thereby deteriorate reliability or high response which is a feature of an ultrasonic motor.
It is an object of the present invention to provide an ultrasonic motor and an electronic apparatus having an ultrasonic motor which is excellent in response or stability in restarting operation and highly reliable.
In order to resolve the above-described problem, according to claim 1, the oscillation drive circuit comprises a power amplifier for amplifying an excitation signal, a capacitive circuit for adjusting a frequency of the oscillation signal, and a switching circuit connected in parallel with a capacitive element constituting the capacitive circuit for shortcircuiting terminals of the capacitive element based on an output signal from the start/stop signal generating means, wherein when the oscillation drive circuit is brought into the stop state based on the output signal from the start/stop signal generating means, the switching circuit is made ON and the terminals of the capacitive element is brought into a shortcircuited state.
According to the invention, electric charge remaining in the capacitive element is discharged in the stop state and in restarting operation, there is provided excellent oscillation rise characteristic by facilitating to form an initial signal constituting the basis of oscillation and the ultrasonic motor and an electronic apparatus having the ultrasonic motor excellent in response and which is highly reliable are realized.
According to the invention described in claim 2, the oscillation drive circuit comprises a power amplifier for amplifying an excitation signal, a capacitive circuit for adjusting a frequency of the excitation signal, and an oscillation starting circuit for generating an oscillation start trigger based on the output signal from the start/stop signal generating means, and wherein the oscillation starting circuit is operated during a rise time period in which the oscillation drive circuit is brought into an active state and starts oscillation based on the output signal from the start/stop signal generating means.
According to the invention, in respect of a high impedance state of an output from the power amplifier which is caused in rise of oscillation which is brought about by a dispersion in semiconductor process regardless of the fact that the power amplifier is brought into an active state, failure in starting to oscillate is avoided by generating the oscillation start trigger during the rise time period of starting the oscillation and there can be realized the ultrasonic motor and an electronic apparatus having the ultrasonic motor with high response and high reliability providing excellent oscillation rise characteristic.
According to the invention described in claim 3, the oscillation drive circuit comprises a power amplifier for amplifying an excitation signal, a capacitive circuit for adjusting a frequency of the excitation signal, a switching circuit connected in parallel with a capacitive element constituting the capacitive circuit for shortcircuiting terminals of the capacitive element based on an output signal from the start/stop signal generating means, and an oscillation starting circuit for generating an oscillation start trigger based on the output signal from the start/stop signal generating means, wherein when the oscillation drive circuit is brought into the stop state based on the output signal from the start/stop signal generating means, the switching circuit is made ON and the terminals of the capacitive element are brought into a shortcircuited state, and wherein when the oscillation drive circuit is brought into an active state based on the output signal from the start/stop signal generating means, the switching circuit is made OFF and the oscillation starting circuit for generating the oscillation start trigger is operated during a rise time period of starting oscillation.
According to the invention, electric charge remaining in the capacitive element is discharged in the stop state and an initial signal constituting a basis of oscillation is facilitated to form in restarting operation and in respect of a high impedance state of an output from the power amplifier caused in rise of oscillation which is brought about by a dispersion in semiconductor process, failure of starting oscillation is avoided by generating the oscillation start trigger during a rise time period of starting oscillation by which there is realized the ultrasonic motor with excellent response and high reliability providing further excellent oscillation rise characteristic and an electronic apparatus having the ultrasonic motor.
According to the invention described in claim 4, the oscillation drive circuit comprises a capacitive circuit for adjusting a frequency of the oscillation signal and the power amplifier constituted by using an inverter at an input unit.
According to the invention, there is realized the ultrasonic motor with excellent response and high reliability avoiding failure of starting oscillation caused by dispersion in semiconductor process and providing excellent oscillation rise characteristic.
According to the invention described in claim 5, the oscillation drive circuit comprises a capacitive circuit for adjusting a frequency of the excitation signal, a switching circuit connected in parallel with a capacitive element constituting the capacitive circuit for shortcircuiting terminals of the capacitive element based on an output signal from the start/stop signal generating means and a power amplifier for amplifying an excitation signal and constituted by using an inverter at an input unit, wherein when the oscillation drive circuit is brought into a stop state based on the output signal from the start/stop signal generating means, the switching circuit is made ON and the terminals of the capacitive element is shortcircuited.
According to the invention, electric charge remaining in the capacitive element is discharged in the stop state, an initial signal constituting a basis of oscillation is facilitated to form in restarting operation and failure of starting oscillation caused by a dispersion in semiconductor process is avoided by which there is realized the ultrasonic motor with excellent response and high reliability providing further excellent oscillation rise characteristic and an electronic apparatus having the ultrasonic motor.
According to the invention described in claim 6, there is provided the ultrasonic motor according to claim 4 or claim 5 wherein the power amplifier of the oscillation drive circuit comprises the inverter installed at the input unit, and a prebuffer installed between the inverter and an output unit, wherein inversion voltages of the inverter of the input unit and the prebuffer is a half of a power source voltage.
According to the invention, the operating point of oscillation is at a half of the power source voltage and accordingly, further excellent oscillation rise characteristic is achieved.
According to the invention described in claim 7, there is provided the ultrasonic motor according to any one of claim 1 through claim 6 wherein two sets of electrode groups comprising a plurality of electrodes are formed on a surface of the piezoelectric element, wherein the oscillation drive circuit includes two power amplifiers output terminals of which are connected respectively to the two sets of electrode groups formed on the surface of the piezoelectric element for driving to oscillate the respective electrode groups independently from each other, and wherein a rotational direction of the moving body is switched by selecting which power amplifier of the two power amplifiers the output terminals of which are connected to the respective two sets of electrode groups formed on the surface of the piezoelectric element is to be brought into an active state based on the output signal from the start/stop signal generating means.
According to the invention, there is provided the ultrasonic motor for switching the rotational direction by selecting to use the two electrode groups of the piezoelectric element and the motor is driven by oscillation by selectively bringing the power amplifier into an active state and therefore, there is provided the ultrasonic motor of a self-excited drive style facilitating oscillation and having excellent oscillation rise characteristic.
According to the invention described in claim 8, there is provided the ultrasonic motor according to claim 7 wherein the two power amplifiers the output terminals of which are connected to the two sets of electrode groups formed on the surface of the piezoelectric element are respectively constituted by a plurality of power amplifying circuits connected in parallel with each other, further comprising output adjusting signal generating means for outputting a signal for adjusting an output impedance of the power amplifier by selecting the power amplifying circuit to be functioned among the plurality of power amplifying circuits.
According to the invention, there is provided the ultrasonic motor switching the rotational direction by selecting to use the two electrode groups of the piezoelectric element and the motor is driven by oscillation by selectively bringing the power amplifier into an active state and accordingly, the output impedance of the power amplifier, that is, the motor output can be adjusted similar to the method of switching start/stop or rotational direction by respectively constituting the plurality of power amplifying circuits where the power amplifiers are connected in parallel with each other. Accordingly, there can be realized the ultrasonic motor of a self-excited oscillation drive style with high function and high reliability capable of optimally driving the motor against a change in load or outer environment.
According to the invention described in claim 9, there is provided the ultrasonic motor according to claim 8, further comprising voltage detecting means for detecting a power source voltage of a power source, and voltage comparing means for comparing the voltage detected by the voltage detecting means with a predetermined power source voltage data.
According to the invention, as a result of comparison by the voltage comparing means, when the voltage detected by the voltage detecting means and the power source voltage data do not coincide with each other, the output impedance of the power amplifier can be adjusted by power adjusting signal generating means and there can be realized the ultrasonic motor of a self-excited drive system with high reliability capable of dealing with the change in the power source voltage or the like.
According to the invention described in claim 10, there is provided the ultrasonic motor according to any one of claim 1 through claim 9 wherein the output impedance of the power amplifier is adjusted by cutting connection of drain sides of output stage transistors of the power amplifier constituting the oscillation drive circuit based on the output signal from the start/stop signal generating means or the output adjusting signal generating means.
According to the invention, switching of start/stop and rotational direction, adjustment of the output impedance of the power amplifier for adjusting the output of the motor can be realized by a very simple circuit constitution and there can be inexpensively realized the ultrasonic motor of a self-excited oscillation drive type with high response and reliability.
According to the invention described in claim 11, there is provided an ultrasonic motor comprising an oscillation drive circuit for generating an oscillation wave by self-excited oscillation by the oscillator bonded with the piezoelectric element, and start/stop signal generating means for generating a signal for controlling start/stop of the ultrasonic motor by bringing the oscillation drive circuit into an active state/stop state, wherein two sets of electrode groups comprising a plurality of electrodes are formed on a surface of the piezoelectric element and the oscillation drive circuit comprises two power amplifiers output terminals of which are connected to respectively the two sets of electrode groups formed on the surface of the piezoelectric element for driving to excite the respective electrode groups independently from each other and a capacitive circuit for adjusting a frequency of an excitation signal wherein a rotational direction of the moving body is switched by selecting which power amplifier of the two power amplifiers the output terminals of which are connected to respectively the two sets of electrode groups formed on the surface of the piezoelectric element is to be brought into an active state, the ultrasonic motor further comprising self-excited oscillation rise controlling means for forming an initial signal in the oscillation drive circuit by bringing both of the two power amplifiers into the active state when the ultrasonic motor is started and bringing either one of the power amplifiers into a stop state and starting driving operation in accordance with the output signal from the start/stop signal generating means after the initial signal has been amplified to the excitation signal by the oscillation drive circuit.
According to the invention, although in driving the motor, only one of the two sets of the electrode groups is used, in rise of oscillation, both of the electrode groups are used and accordingly, the loop gain of the oscillation drive circuit becomes high and the oscillation rise time period is considerably shortened and there is realized the ultrasonic motor in which the reliability in rise of oscillation is promoted and the response is excellent and an electronic apparatus having the ultrasonic motor.
According to the invention described in claim 12, there is provided the ultrasonic motor according to any one of claim 1 through claim 11 wherein the oscillation drive circuit includes a resonating circuit constituted by the oscillator and the capacitive element by utilizing an inductive property provided to the oscillator bonded with the piezoelectric element in a mechanical resonance state.
According to the invention, the mechanical resonance of the oscillator is sharp and accordingly, there can be constituted the oscillation drive circuit which is excellent in the performance of selecting frequency and is provided with excellent stability.
According to the invention described in claim 13, there is provided the ultrasonic motor according to any one of claim 1 through claim 12 wherein the piezoelectric element is formed with electrodes of a multiple of 4 substantially at equal intervals on the at least one surface and subjected to a polarization treatment in which contiguous two electrodes are paired and a direction of the polarization treatment is reversed at each pair, further comprising first connecting means and second connecting means for constituting the two sets of electrode groups by electrically shortcircuiting every other electrode, and projections for transmitting a power to the moving body at positions of vicinities of every other boundary of the electrodes formed by the multiple of 4 substantially at equal intervals on the at least one plane of the piezoelectric element on one surface of the oscillator.
According to the invention, there is provided the ultrasonic motor of a single phase drive capable of switching the rotational direction by selecting the two sets of the electrode groups and there is achieved an effect of significantly simplifying the constitution of the oscillation drive circuit owing to the single phase drive.
According to the invention of claim 14, there is provided the ultrasonic motor according to any one of claim 1 through claim 13, further comprising rotational information detecting means for detecting a rotational state of the moving body, and an electrostatic capacity adjusting circuit as rotational number controlling means for adjusting a rotational number of the moving body based on an output signal from the rotational information detecting means.
According to the invention, there can be realized the ultrasonic motor having high stability against drive environment, load variation or the like only by adjusting the electrostatic capacitance by the capacitive circuit of the oscillation drive circuit.
According to the invention of claim 15, there is provided an electronic apparatus having an ultrasonic motor comprising the ultrasonic motor described in any one of claim 1 through claim 14.
According to the invention, there can be constituted the electronic apparatus with higher function and higher reliability by the feature provided to the ultrasonic motor.